The present invention relates to an actuation device, in particular with actuation by an electromagnet.
European Published Patent Application No. 0 270 536 describes an actuation device for a valve which can be actuated electrically and with which a precisely predeterminable parameter can be obtained despite the use of components with customary tolerances of the basic air gap. For this purpose, a return plate is secured, as an adjustable part, to a housing by means of a return spring. The actuation device contains a magnet core as a fixed part. The return spring is secured to a pin and the adjustable part is connected to the pin. The pin has a collar. The return spring is clamped in between the collar and a spring which bears against the adjustable part. In the non-actuating state there is a precisely determined basic air gap between the adjustable part and the fixed part. The basic air gap can be varied by pressing a suitable connection, for example the pin in the adjustable part, to a greater or lesser extent. In this way, the component tolerances can easily be compensated.
If such an actuation device is installed, for example, in a steering valve, which can be actuated electrically, of a power steering system, in particular of a motor vehicle, it is not possible to change the valve characteristic curve. After the dimensions of the actuation device and of the steering valve have been specified, the valve characteristic curve is definitively specified.
It is an object of the present invention to provide an actuation device so that it is possible to adjust the valve characteristic curve of a steering valve after the power steering system has been mounted.
The above and other beneficial objects of the present invention are achieved by providing an actuation device as described herein. By providing an adjustable collar, the basic air gap may be adjusted even after the actuation device is mounted, for example, in an electro-hydraulic transducer of a steering valve. In this manner, the valve characteristic curve may be adjusted and a narrower tolerance band may be achieved at the steering valve. The valve characteristic curve may be placed in a certain, desired tolerance range.
The adjustable collar may easily be formed by a nut which may be adjusted by a thread which is arranged on the pin. In order to be able to set the basic air gap when the steering valve is completely mounted, an opening is provided in the closure cover, which may be closed off by a cover. The nut of the collar is easily accessible through the opening.